Preparation method of bio-based environment-friendly flame retardant and flame-retardant modified natural rubber of bio-based environment-friendly flame retardant

Abstract

The invention relates to the technical field of flame retardants, in particular to a preparation method of a bio-based environment-friendly flame retardant and flame-retardant modified natural rubber of the bio-based environment-friendly flame retardant. The preparation method comprises the following steps: selecting raw materials and carrying out an operation treatment reaction based on the selected raw materials, based on a selected raw material operation treatment reaction method, a polyhydroxy bio-based monomer is selected to react with a phosphorus-containing monomer to prepare a bio-based flame retardant; or a multi-amino bio-based monomer is selected to react with a phosphorus-containing monomer to prepare a bio-based flame retardant, and the prepared bio-based flame retardant is mixed with the natural rubber to prepare the flame-retardant natural rubber composite material, so that the flame-retardant property of the natural rubber is improved, and the mechanical property of the natural rubber is ensured not to be lost.

Description

Technical Field

[0001] The present invention relates to the technical field of flame retardants, and specifically to a preparation method of a bio-based environmentally friendly flame retardant and its flame-retardant modification of natural rubber. Background Art

[0002] As a natural polymer material, natural rubber occupies an important position in the fields of tire manufacturing, medical devices, shock-absorbing components, conveyor belts, etc. due to its excellent elasticity, abrasion resistance, tear resistance and renewable characteristics. Its molecular chain is composed of cis-1,4-polyisoprene, which endows the material with high resilience and low hysteresis loss, and at the same time has good alkali resistance and processing performance. With the increasing demand for green materials, natural rubber, as a sustainable resource, has been continuously extended to emerging fields such as new energy vehicles and smart wearable devices. However, its inherent defect - the limiting oxygen index (LOI) is only about 17, belonging to a flammable material - severely restricts its application in high-temperature and high-safety scenarios. For example, in the encapsulation of electronic devices or building fireproof materials, the flammability of natural rubber is likely to cause fire hazards, and it is urgent to improve its safety performance through flame-retardant modification.

[0003] Currently, the flame-retardant modification of natural rubber mainly relies on additive flame retardants, but the existing technologies have significant limitations: on the one hand, although traditional halogen-based flame retardants (such as decabromodiphenylethane) have high flame-retardant efficiency, they will release toxic gases such as hydrogen halide during combustion, violating the requirements of environmental protection regulations, while inorganic flame retardants (such as aluminum hydroxide) need a high addition amount (30%-60%) to reach the UL94 V-0 level, resulting in an increase in material density and deterioration of mechanical properties (such as a 20%-40% decrease in tensile strength); on the other hand, conventional halogen-free flame retardants (such as ammonium polyphosphate, melamine, etc.) have low flame-retardant efficiency in polyolefin matrices, and the preparation raw materials are severely dependent on petrochemical products; in addition, although emerging nano-composite flame retardant systems (such as attapulgite / graphene synergistic systems) can improve the dispersibility, their raw materials still rely on non-renewable mineral resources, the preparation process has high energy consumption, and the biodegradability is poor. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a preparation method of a bio-based environmentally friendly flame retardant and its flame-retardant modification of natural rubber, develop an efficient flame retardant based on biomass raw materials, improve its compatibility with the rubber matrix through molecular design, and utilize the bio-based components in the solid-phase and gas-phase synergistic flame-retardant mechanism, which becomes the key to breaking through the bottleneck of the existing technology and provides a green solution for the high-value application of natural rubber.

[0005] To achieve the above purpose, the present invention provides the following technical solution: A preparation method of a bio-based environmentally friendly flame retardant, including raw material selection and operation and treatment reactions based on the selected raw materials. The raw materials include polyhydroxy biobased monomers, polyamino biobased monomers and phosphorus-containing monomers. Based on the selected raw materials, the operation and treatment reaction method is to react the polyhydroxy biobased monomer with the phosphorus-containing monomer to obtain a biobased flame retardant; or react the polyamino biobased monomer with the phosphorus-containing monomer to obtain a biobased flame retardant.

[0006] In some embodiments, the phosphorus-containing monomer is diphenyl chlorophosphate or diphenylphosphoryl chloride. The polyhydroxy biobased monomer or polyamino biobased monomer reacts with diphenyl chlorophosphate or diphenylphosphoryl chloride respectively to obtain a biobased flame retardant.

[0007] In some embodiments, the polyhydroxy biobased monomer is ellagic acid or catechin. Reacting the polyhydroxy biobased monomer with the phosphorus-containing monomer to obtain a biobased flame retardant includes: Ellagic acid and diphenyl chlorophosphate react in a molar ratio of 1:2 to obtain a biobased flame retardant. Ellagic acid and diphenylphosphoryl chloride react in a molar ratio of 1:2 to obtain a biobased flame retardant. Catechin and diphenyl chlorophosphate react in a molar ratio of 1:3 to obtain a biobased flame retardant. Catechin and diphenylphosphoryl chloride react in a molar ratio of 1:3 to obtain a biobased flame retardant.

[0008] In some embodiments, the polyamino biobased monomer is spermidine or L-arginine. Reacting the polyamino biobased monomer with the phosphorus-containing monomer to obtain a biobased flame retardant includes: Spermidine and diphenyl chlorophosphate react in a molar ratio of 1:1 to obtain a biobased flame retardant. Spermidine and diphenylphosphoryl chloride react in a molar ratio of 1:1 to obtain a biobased flame retardant. L-arginine and diphenyl chlorophosphate react in a molar ratio of 1:1 to obtain a biobased flame retardant. L-arginine and diphenylphosphoryl chloride react in a molar ratio of 1:1 to obtain a biobased flame retardant.

[0009] In some embodiments, the preparation method of reacting ellagic acid with the phosphorus-containing monomer to obtain a biobased flame retardant is as follows: Dissolve a preset amount of ellagic acid and the phosphorus-containing monomer in tetrahydrofuran respectively to obtain corresponding solutions, where the molar ratio of ellagic acid to the phosphorus-containing monomer is 1:2. Add the ellagic acid solution into a container, and at the same time, drop the phosphorus-containing monomer solution into the ellagic acid solution drop by drop through a constant pressure dropping funnel, and control the reaction temperature at 0-5 °C by an ice-water bath. After the addition of the phosphorus-containing monomer solution is completed, raise the reaction temperature to 80 - 120 °C and react for 5 - 10 h; After the reaction is completed, drop the solution in the container into ethyl acetate, and the reaction product will precipitate and settle. The bio-based flame retardant is obtained by filtration, washing with water, and drying.

[0010] In some of these embodiments, the preparation method of the bio-based flame retardant prepared by reacting catechin with a phosphorus-containing monomer is as follows: Dissolve a preset amount of catechin and a phosphorus-containing monomer in tetrahydrofuran respectively to obtain corresponding solutions, where the molar ratio of catechin to the phosphorus-containing monomer is 1:3; Add the catechin solution to a container, and at the same time, drop the phosphorus-containing monomer solution into the catechin solution drop by drop through a constant-pressure dropping funnel, and control the reaction temperature at 0 - 5 °C by an ice-water bath; After the addition of the phosphorus-containing monomer solution is completed, raise the reaction temperature to 80 - 120 °C and react for 5 - 10 h; After the reaction is completed, drop the solution in the container into ethyl acetate, and the reaction product will precipitate and settle. The bio-based flame retardant is obtained by filtration, washing with water, and drying.

[0011] In some of these embodiments, the preparation method of the bio-based flame retardant prepared by reacting spermidine with a phosphorus-containing monomer is as follows: Dissolve a preset amount of spermidine and a phosphorus-containing monomer in toluene respectively to obtain corresponding solutions, where the molar ratio of spermidine to the phosphorus-containing monomer is 1:1; Add the spermidine solution to a container, and at the same time, drop the phosphorus-containing monomer solution into the spermidine solution drop by drop through a constant-pressure dropping funnel, and control the reaction temperature at 0 - 5 °C by an ice-water bath; After the addition of the phosphorus-containing monomer solution is completed, raise the reaction temperature to 80 - 120 °C and react for 5 - 10 h; After the reaction is completed, drop the solution in the container into ethyl acetate, and the reaction product will precipitate and settle. The bio-based flame retardant is obtained by filtration, washing with water, and drying.

[0012] In some of these embodiments, the preparation method of the bio-based flame retardant prepared by reacting L-arginine with a phosphorus-containing monomer is as follows: Dissolve a certain amount of L-arginine and a phosphorus-containing monomer in toluene respectively to obtain corresponding solutions, where the molar ratio of L-arginine to the phosphorus-containing monomer is 1:1; Add the L-arginine solution to a container, and at the same time, drop the phosphorus-containing monomer solution into the L-arginine solution drop by drop through a constant-pressure dropping funnel, and control the reaction temperature at 0 - 5 °C by an ice-water bath; After the addition of the phosphorus-containing monomer solution is completed, raise the reaction temperature to 80 - 120 °C and react for 5 - 10 h; After the reaction is completed, the solution in the container is dropped into ethyl acetate, and the reaction product precipitates and settles. The bio-based flame retardant is prepared by filtration, washing with water, and drying.

[0013] To achieve the above object, the present invention also provides the following technical solution: A flame-retardant modified natural rubber based on a bio-based environmentally friendly flame retardant is prepared by mixing a bio-based flame retardant prepared by the preparation method of a bio-based environmentally friendly flame retardant with natural rubber to obtain a flame-retardant natural rubber composite material.

[0014] In some of the embodiments, the specific preparation method of the flame-retardant natural rubber composite material is as follows: Plasticize the natural rubber raw rubber on an open mill at 80-100 °C for 10-20 min; Then add 1-2 parts of stearic acid, 4-6 parts of zinc oxide, 0.5-1 part of antioxidant, and 1-2 parts of accelerator, and continue to knead on the open mill until the rubber compound is uniform; Next, add 5-15 parts of the bio-based flame retardant to the rubber compound, continue to knead for 20-40 min, the roller speed is 150-200 rpm, and then cool to 50-60 °C; Add 1-3 parts of vulcanizing agent and 10-20 parts of carbon black, and continue to knead for 15-20 min; Finally, vulcanize at 140-160 °C on a flat vulcanizer for 5-10 min, and the pressure is 5-15 MPa to obtain the flame-retardant natural rubber composite material.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. The flame retardant prepared by the present invention uses bio-based raw materials in the synthesis, reduces carbon emissions during the production process of the flame retardant, and provides the sustainability of the flame retardant; 2. The bio-based flame retardant prepared in the present invention can significantly improve the flame retardancy of natural rubber. Relying on the free radical capture effect of the flame retardant in the gas phase and the charring effect in the condensed phase, adding only 15 parts can make the natural rubber composite material exhibit excellent flame retardant properties, such as the vertical burning grade reaching V-0 and the limiting oxygen index (LOI) increasing to 29%; 3. The bio-based flame retardant prepared in the present invention can have a strong interfacial bonding force with the matrix through interfacial modification, so the mechanical properties of the natural rubber composite material are maintained well.

[0016] Details of one or more embodiments of the present application are set forth in the following drawings and description, so that other features, objects, and advantages of the present application will become more concise and understandable. The present application is described in detail and understood through the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the infrared spectrum diagram of the product in Example 1; Figure 2 It is the synthetic route diagram of Example 1; Figure 3 It is the synthetic route diagram of Example 2; Figure 4 It is the synthetic route diagram of Example 3; Figure 5 It is the synthetic route diagram of Example 4; Figure 6 It is the synthetic route diagram of Example 5; Figure 7 It is the synthetic route diagram of Example 6; Figure 8 It is the synthetic route diagram of Example 7; Figure 9 It is the synthetic route diagram of Example 8. Detailed implementation manners

[0018] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0019] In the traditional existing natural rubber flame retardant modification system, the contradiction between the raw material sustainability defect and the flame retardant efficiency of petroleum-based flame retardants is prominent. The hydrogen halide released by halogen-based flame retardants during combustion not only corrodes equipment components but also triggers the smoke toxicity alarm system, while the high filling amount of inorganic flame retardants leads to an abnormal increase in the elastic modulus of rubber materials, and stress concentration cracks are likely to occur under dynamic load conditions. More critically, the raw material synthesis path of the traditional flame retardant modification system relies on non-renewable carbon sources, which fundamentally conflicts with the green manufacturing concept of bio-based polymer materials.

[0020] For example, during the manufacturing process of the sealing gasket of a new energy vehicle power battery pack, traditional flame retardant modified natural rubber needs to simultaneously meet the UL94 V-0 flame retardant grade and an elongation at break of more than 80%. It is found in actual production that when the addition amount of aluminum hydroxide reaches 50%, the Mooney viscosity of the mixed rubber compound rises to 90 ML(1+4)125°C, resulting in melt fracture during extrusion molding. At the same time, interface debonding is caused by filler agglomeration during the vulcanization stage, and the Shore hardness of the final product exceeds 75 HA, and it cannot pass the 100,000-cycle dynamic compression fatigue test. This phenomenon is particularly significant in high-temperature and high-humidity environments, and the residual halogen impurities inside the material will also accelerate the electrochemical corrosion of copper electrode joints.

[0021] If the above problems are not solved, the sealing components of the new energy vehicle power system will be forced to adopt a metal-rubber composite structure, resulting in an 8%-12% increase in the vehicle's overall mass, which directly affects the cruising range index. More seriously, the traditional flame retardant raw material supply chain and the bioeconomy industrial chain cannot form a closed loop, and an additional 25%-30% of implicit carbon emissions will be generated in the life cycle assessment. This not only violates the EU REACH regulation's restrictions on persistent organic pollutants but also makes it difficult to pass the ISO 14067 carbon footprint certification.

[0022] When facing the above problems, this application first analyzes the dual negative impacts of traditional flame retardants on material mechanical properties and environmental friendliness, and finds that the core contradiction lies in the non-renewability of raw materials and insufficient flame retardant efficiency. To solve this contradiction, this application attempts to screen active monomers from bio-based raw materials that can form stable chemical bonds with phosphorus-containing compounds. Among them, the polyhydroxy or polyamino structure is given priority due to its rich reaction sites. By comparing different reaction paths, it is found that the condensation reaction of polyhydroxy bio-based monomers and phosphorus-containing monomers can construct a phosphorus-oxygen covalent bond, while the polycondensation reaction of polyamino bio-based monomers and phosphorus-containing monomers forms a phosphorus-nitrogen synergistic flame retardant structure. Both paths can avoid the problem of filler agglomeration caused by traditional physical blending. Finally, polyhydroxy and polyamino bio-based monomers are selected as independent reaction systems respectively, and by precisely controlling the molar ratio of reactants, phosphorus elements are introduced at the molecular level to form bio-based flame retardants with intrinsic flame retardant properties.

[0023] In this regard, the present invention proposes a preparation method of a bio-based environmentally friendly flame retardant, including raw material selection and operation and treatment reactions based on the selected raw materials. The raw materials include polyhydroxy bio-based monomers, polyamino bio-based monomers, and phosphorus-containing monomers. The operation and treatment reaction method based on the selected raw materials is to select polyhydroxy bio-based monomers and phosphorus-containing monomers to react to obtain a bio-based flame retardant; or select polyamino bio-based monomers and phosphorus-containing monomers to react to obtain a bio-based flame retardant.

[0024] Among them, the polyhydroxy bio-based monomer refers to a bio-based source compound containing two or more hydroxyl functional groups. Specifically, it can be realized by polyphenolic compounds extracted from plants. Its hydroxyl functional groups can undergo esterification or condensation reactions with phosphorus-containing monomers to form a phosphorus-containing flame retardant structure, improving the flame retardant efficiency of natural rubber.

[0025] Among them, the polyamino bio-based monomer refers to a bio-based source compound containing two or more amino functional groups. Specifically, it can be realized by amine compounds in animal or microbial metabolites. Its amino functional groups can undergo condensation or substitution reactions with phosphorus-containing monomers to introduce a phosphorus-nitrogen synergistic flame retardant effect and enhance the flame retardant performance.

[0026] Among them, the phosphorus-containing monomer refers to a compound containing phosphorus element and having active reactive groups, and specifically, organic phosphate esters or phosphoryl chloride compounds can be used to achieve this. During the combustion process, the phosphorus element in it generates a phosphoric acid layer to isolate oxygen and inhibits flame propagation through a gas-phase free radical quenching mechanism.

[0027] The operation and treatment reaction method is the reaction of polyhydroxy biobased monomers with phosphorus-containing monomers, or the reaction of polyamino biobased monomers with phosphorus-containing monomers. Specifically, directional condensation can be achieved by controlling the molar ratio of hydroxyl or amino groups to phosphorus-containing monomers, forming a stable molecular structure of the biobased flame retardant and avoiding the high dosage requirements of traditional flame retardants.

[0028] The core innovation of this application lies in using the reaction of polyhydroxy or polyamino biobased monomers with phosphorus-containing monomers to construct a molecular structure with both biobased environmental protection characteristics and high flame retardant performance. The compatibility between the flame retardant and the natural rubber matrix is improved through the chemical bonding of hydroxyl / amino groups with phosphorus-containing functional groups, while avoiding the toxicity and non-renewability problems of petroleum-based flame retardants.

[0029] The working process and principle of this application are as follows. The preparation method of this biobased environmental protection flame retardant includes two main steps: raw material selection and operation and treatment reaction based on the selected raw materials. In the raw material selection stage, three types of key raw materials are determined: polyhydroxy biobased monomers, polyamino biobased monomers, and phosphorus-containing monomers. The selection of these raw materials provides the necessary reactants for subsequent reactions.

[0030] In the operation and treatment reaction stage, two reaction paths are adopted: one is to select polyhydroxy biobased monomers to react with phosphorus-containing monomers; the other is to select polyamino biobased monomers to react with phosphorus-containing monomers. Both of these reaction paths can produce biobased flame retardants.

[0031] The reaction of polyhydroxy biobased monomers with phosphorus-containing monomers utilizes the condensation reaction between hydroxyl groups and phosphorus-containing groups to form a phosphorus-oxygen covalent bond. The reaction of polyamino biobased monomers with phosphorus-containing monomers constructs a phosphorus-nitrogen synergistic flame retardant structure through the polycondensation reaction between amino groups and phosphorus-containing groups. Both of these reaction mechanisms introduce phosphorus elements at the molecular level, endowing the product with intrinsic flame retardant properties.

[0032] By selecting different biobased monomers to react with phosphorus-containing monomers, the structure and properties of the final flame retardant can be regulated. The polyhydroxy path is beneficial to improving the thermal stability of the flame retardant, while the polyamino path helps to improve the charring property of the flame retardant. The design of the two reaction paths provides flexibility for the preparation of biobased flame retardants with different properties.

[0033] Through the above scheme, the biobased environmental protection flame retardant prepared in this application has the following technical effects: First, this flame retardant uses renewable bio-based raw materials, avoiding dependence on petroleum resources and conforming to the concept of sustainable development. Second, by introducing phosphorus through molecular design, intrinsic flame retardancy is achieved, and good flame retardant effects can be obtained without high filling amounts, overcoming the adverse effects of traditional inorganic flame retardants on the mechanical properties of materials. Moreover, this flame retardant does not contain halogens and will not release toxic gases during combustion, meeting environmental protection requirements. Finally, the chemical reaction preparation method of bio-based monomers and phosphorus-containing monomers avoids the problem of filler agglomeration caused by physical blending and is conducive to the uniform dispersion of the flame retardant in the matrix. This bio-based environmentally friendly flame retardant provides a new technical path for the flame retardant modification of polymer materials such as natural rubber and is expected to be widely used in fields such as electronic packaging and building fire protection.

[0034] In practical applications, its phosphorus-containing monomer is diphenyl chlorophosphate or diphenylphosphoryl chloride, As highly reactive phosphorus sources, the phenyl structures of diphenyl chlorophosphate and diphenylphosphoryl chloride can enhance the π-π interaction with bio-based monomers and promote the condensation reaction. The phosphorus contents of the two phosphorus-containing monomers are 9.8% and 10.2% respectively, ensuring that the phosphorus element loading of the final product meets the standard.

[0035] Its polyhydroxy bio-based monomer is ellagic acid or catechin, The hydroxyl groups of ellagic acid or catechin form P-O-C bonds with the chlorine atoms of the phosphorus-containing monomer through nucleophilic substitution reactions; the hydroxyl monomers react with the phosphorus-containing monomers to ensure full cross-linking of functional groups.

[0036] Its polyamino bio-based monomer is spermidine or L-arginine, The amino groups of spermidine or L-arginine generate P-N-C bonds with the chlorine atoms of the phosphorus-containing monomer through condensation reactions; the amino monomers react with the phosphorus-containing monomers to ensure full cross-linking of functional groups. Based on the above raw materials, a total of 8 bio-based flame retardants can be reacted to form, namely: Bio-based flame retardant prepared from ellagic acid + diphenyl chlorophosphate, bio-based flame retardant prepared from ellagic acid + diphenylphosphoryl chloride; Bio-based flame retardant prepared from catechin + diphenyl chlorophosphate, bio-based flame retardant prepared from catechin + diphenylphosphoryl chloride; Bio-based flame retardant prepared from spermidine + diphenyl chlorophosphate, bio-based flame retardant prepared from spermidine + diphenylphosphoryl chloride; Bio-based flame retardant prepared from L-arginine + diphenyl chlorophosphate, bio-based flame retardant prepared from L-arginine + diphenylphosphoryl chloride.

[0037] Specifically, the benzene ring structures of diphenyl chlorophosphate and diphenylphosphoryl chloride can reduce steric hindrance, making the hydroxyl or amino groups of the bio-based monomers more accessible to the reaction sites. When ellagic acid or catechin is used as a polyhydroxy monomer, its four phenolic hydroxyl groups react with two molecules of phosphorus-containing monomers to form a tetrasubstituted phosphate ester structure; when spermidine or L-arginine is used as a polyamino monomer, three amino groups combine with three molecules of phosphorus-containing monomers to form a three-dimensional network structure.

[0038] During the reaction process, the chlorine atom of the phosphorus-containing monomer acts as a leaving group and undergoes polycondensation with the bio-based monomer in a tetrahydrofuran or toluene solvent. The reaction temperature is controlled in a gradient manner: initially at 0 - 5 °C to avoid local overheating caused by intense exothermic reactions, and then heated to 80 - 120 °C to accelerate the growth of molecular chains. The product is purified by precipitation with ethyl acetate to remove unreacted monomers and by-products. Finally, the phosphorus content of the prepared flame retardant is stably in the range of 8.5% - 9.6%, and the thermal decomposition temperature exceeds 300 °C, meeting the processing temperature requirements of natural rubber. Based on the 8 bio-based flame retardants described above, the following are the example cases: Example 1: Ellagic acid + diphenyl chlorophosphate According to Figure 2 the shown synthesis route, a certain amount of ellagic acid and diphenyl chlorophosphate are respectively dissolved in 100 ml of tetrahydrofuran, and the molar ratio of ellagic acid to diphenyl chlorophosphate is 1:2; the ellagic acid solution is added to a round-bottom flask, and at the same time, the diphenyl chlorophosphate solution is gradually dropped into the ellagic acid solution through a constant-pressure dropping funnel, and the reaction temperature is controlled at 0 - 5 °C by an ice-water bath; after the diphenyl chlorophosphate solution is completely dropped, the reaction temperature is raised to 80 - 120 °C and reacted for 5 - 10 h; after the reaction is completed, the solution in the flask is dropped into ethyl acetate, and the reaction product precipitates and settles. Through steps such as filtration, washing with water, and drying, the final bio-based phosphorus-based flame retardant is obtained.

[0039] The ellagic acid molecule contains four phenolic hydroxyl groups. Using a 1:2 molar ratio can enable two molecules of phosphorus-containing monomers to undergo esterification or condensation reactions with two of its hydroxyl groups respectively, ensuring sufficient reaction and a symmetric product structure, ensuring that each phosphorus-containing monomer molecule only reacts with two hydroxyl groups of ellagic acid, and avoiding insolubility or decreased thermal stability of the product caused by crosslinking or over-substitution.

[0040] As Figure 1 shown in the infrared spectrum of the synthesis product of Example 1, the characteristic groups of ellagic acid itself can be seen, such as hydroxyl (3477 cm-1), carbonyl (1729 cm-1), and benzene ring skeleton peaks (1500 - 1650 cm-1), the P=O of diphenyl chlorophosphate itself (1258 cm-1), and the newly produced phosphate ester bond P−O (919 cm-1), proving the successful synthesis of this bio-based flame retardant. Example 2: Ellagic acid + diphenylphosphoryl chloride The synthesis preparation steps are the same as those in Example 1, replacing diphenyl chlorophosphate with diphenylphosphoryl chloride, and the synthesis route is as Figure 3 shown. Example 3: Catechin + diphenyl chlorophosphate According to Figure 4 the shown synthesis route, a certain amount of catechin and diphenyl chlorophosphate are respectively dissolved in 100 ml of tetrahydrofuran, where the molar ratio of catechin to diphenyl chlorophosphate is 1:3; the catechin solution is added to a round-bottom flask, and at the same time, the diphenyl chlorophosphate solution is gradually dropped into the catechin solution through a constant-pressure dropping funnel, and the reaction temperature is controlled at 0-5 °C by an ice-water bath; after the diphenyl chlorophosphate solution is completely dropped, the reaction temperature is raised to 80-120 °C, and the reaction is carried out for 5-10 h; after the reaction is completed, the solution in the flask is dropped into ethyl acetate, and the reaction product precipitates and settles. Through steps such as filtration, washing with water, and drying, the final bio-based phosphorus-based flame retardant is obtained.

[0041] The catechin molecule contains three hydroxyl groups. A molar ratio of 1:3 can enable all three hydroxyl groups to participate in the reaction, avoiding the influence of unreacted hydroxyl group residues on the flame retardant performance. The 1:3 ratio of catechin to the phosphorus-containing monomer utilizes its catechol structure, and the three hydroxyl groups react with three phosphorus-containing monomers in sequence to form a trisubstituted product, maximizing the introduction amount of phosphorus element to improve the flame retardant efficiency.

[0042] Example 4: Catechin + diphenylphosphoryl chloride The synthesis preparation steps are the same as those in Example 3, replacing diphenyl chlorophosphate with diphenylphosphoryl chloride, and the synthesis route is as Figure 5 shown. Example 5: Spermidine + diphenyl chlorophosphate According to Figure 6 the shown synthesis route, a certain amount of spermidine and diphenyl chlorophosphate are respectively dissolved in 100 ml of toluene, where the molar ratio of spermidine to diphenyl chlorophosphate is 1:1; the spermidine solution is added to a round-bottom flask, and at the same time, the diphenyl chlorophosphate solution is gradually dropped into the spermidine solution through a constant-pressure dropping funnel, and the reaction temperature is controlled at 0-5 °C by an ice-water bath; after the diphenyl chlorophosphate solution is completely dropped, the reaction temperature is raised to 80-120 °C, and the reaction is carried out for 5-10 h; after the reaction is completed, the solution in the flask is dropped into ethyl acetate, and the reaction product precipitates and settles. Through steps such as filtration, washing with water, and drying, the final bio-based phosphorus-nitrogen-based flame retardant is obtained.

[0043] Spermidine contains multiple amino functional groups and can undergo an efficient condensation reaction with the phosphoryl chloride group of the phosphorus-containing monomer. When the molar ratio of spermidine to the phosphorus-containing monomer is 1:1, the molar numbers of the amino group and the phosphoryl chloride group match, avoiding the residue of unreacted monomers; when using a 1:1 molar ratio, the amino group and the phosphoryl chloride group react completely, the molecular weight distribution of the product is narrow, and the thermal stability of the flame retardant is improved.

[0044] Example 6: Spermidine + Diphenylphosphoryl Chloride The synthesis preparation steps are the same as those in Example 5, replacing diphenyl phosphorochloridate with diphenylphosphoryl chloride, and the synthesis route is as Figure 7 shown. Example 7: L-Arginine + Diphenyl Phosphorochloridate According to Figure 8 the shown synthesis route, a certain amount of L-arginine and diphenyl phosphorochloridate are respectively dissolved in 100 ml of toluene, where the molar ratio of L-arginine to diphenyl phosphorochloridate is 1:1; the L-arginine solution is added to a round-bottom flask, and at the same time, the diphenyl phosphorochloridate solution is gradually dropped into the L-arginine solution through a constant-pressure dropping funnel, and the reaction temperature is controlled at 0 - 5 °C by an ice-water bath; after the diphenyl phosphorochloridate solution is completely dropped, the reaction temperature is raised to 80 - 120 °C, and the reaction is carried out for 5 - 10 h; after the reaction is completed, the solution in the flask is dropped into ethyl acetate, and the reaction product precipitates and settles. Through steps such as filtration, washing with water, and drying, the final bio-based phosphorus-nitrogen flame retardant is obtained.

[0045] The primary amine and guanidine group of L-arginine participate in the reaction simultaneously to form a cross-linked structure. The rigid molecular structure of L-arginine enhances the interfacial compatibility between the flame retardant and natural rubber, and is uniformly dispersed in the rubber matrix during the subsequent mixing process, improving the flame retardancy efficiency.

[0046] Example 8: L-Arginine + Diphenylphosphoryl Chloride The synthesis preparation steps are the same as those in Example 7, replacing diphenyl phosphorochloridate with diphenylphosphoryl chloride, and the synthesis route is as Figure 9 shown. Example 9: Preparation of Flame-Retardant Natural Rubber Composite Based on the bio-based flame retardants prepared in Examples 1 to 8, a flame-retardant natural rubber composite is prepared by mixing with natural rubber.

[0047] The specific preparation method is as follows: Plasticize the natural rubber raw rubber on an open mill at 80 - 100 °C for 10 - 20 min; Then add stearic acid (1 - 2 parts), zinc oxide (4 - 6 parts), antioxidant (0.5 - 1 part), accelerator (1 - 2 parts), and continue to open mill until the rubber compound is uniform; Next, a bio-based flame retardant (5 - 15 parts) is added to the rubber compound, and mixing is continued for 20 - 40 min at a roller speed of 150 - 200 rpm, and then it is cooled to 50 - 60 °C; A vulcanizing agent (1 - 3 parts of sulfur) and carbon black (10 - 20 parts) are added, and mixing is continued for 15 - 20 min; Finally, it is vulcanized on a flat vulcanizer at 140 - 160 °C for 5 - 10 min under a pressure of 5 - 15 MPa to obtain the flame-retardant natural rubber composite of the present invention.

[0048] Among them, the temperature in the plasticizing stage of the mixing mill is set at 80 - 100 °C. At this time, the movement ability of the natural rubber molecular segments is enhanced, but the degradation temperature threshold is not reached, which not only ensures the plasticizing efficiency but also avoids the decrease in molecular weight; the plasticizing time of 10 - 20 min ensures that the rubber is fully softened to form a continuous phase. The addition amount of stearic acid is controlled at 1 - 2 parts to improve the filler dispersion, 4 - 6 parts of zinc oxide is used as a vulcanization activator, 0.5 - 1 part of antioxidant inhibits the thermal-oxidative aging during mixing, and 1 - 2 parts of accelerator adjusts the vulcanization speed. The bio-based flame retardant is added after the plasticization of the rubber compound. At this time, the rubber matrix has formed a three-dimensional network. Shearing force is provided by a roller speed of 150 - 200 rpm to promote the dispersion of the flame retardant, and the mixing time of 20 - 40 min ensures that the flame retardant is evenly embedded in the gaps between the rubber molecular chains. Cooling to 50 - 60 °C avoids the thermal decomposition of the flame retardant. In the vulcanization stage, high temperature of 140 - 160 °C and pressure of 5 - 15 MPa are adopted to enable the vulcanizing agent to rapidly initiate cross-linking reactions. 10 - 20 parts of carbon black is used as a reinforcing agent to fill the voids in the cross-linked network, forming a dense barrier layer.

[0049] Specifically, in the plasticizing stage, stepwise temperature control is adopted. The initial high-temperature plasticization makes the natural rubber molecular chains fully stretch, and then the temperature is maintained during the addition of additives to prevent the premature activation of zinc oxide. The flame retardant is added after the rubber compound is homogenized, and nano-scale dispersion is achieved through high speed and long mixing time, avoiding the agglomeration of the flame retardant due to premature addition and heat in the traditional process. After the temperature in the cooling stage drops to 50 - 60 °C, the vulcanizing agent is added to prevent the premature decomposition of the vulcanizing agent. Under the conditions of high temperature and high pressure in the flat vulcanization stage, the vulcanizing agent rapidly cross-links with the rubber molecules. The physical cross-linking points formed by the filling of carbon black and the phosphorus-nitrogen synergistic flame retardant effect of the flame retardant jointly construct a three-dimensional barrier structure. At high temperature, this structure can release phosphoric acid to promote carbonization, and at the same time decompose to generate inert gases to dilute oxygen, realizing a dual flame retardant mechanism in the gas phase and the condensed phase. The pressure parameter of 5 - 15 MPa ensures that there are no bubble defects inside the composite material, and the vulcanization time of 5 - 10 min balances the cross-linking density and production efficiency, and finally a natural rubber composite with a flame retardancy rating of UL94 V-0 and a tensile strength retention rate of ≥85% is prepared.

[0050] This solution realizes the uniform dispersion of the bio-based flame retardant in the natural rubber matrix. By optimizing the mixing and vulcanization process parameters, it ensures that the flame-retardant components form a stable cross-linked network inside the material, effectively suppressing the release of heat and smoke during combustion, while avoiding significant impact on the original mechanical properties of the material. This preparation method improves the flame retardancy of natural rubber while avoiding the material degradation problems caused by high temperature or high pressure in traditional flame retardant processes, and no toxic by-products are generated throughout the process. Through the technical solution of the present invention, the properties of natural rubber composites prepared by the flame retardants of Examples 1 to 8 respectively are as follows. The addition amount of the flame retardant is 15 parts in each case, and the actual test data are shown in the following table:

[0051] 1. The flame retardant prepared in the present invention uses bio-based raw materials in the synthesis, reducing carbon emissions during the production process of the flame retardant and providing the sustainability of the flame retardant.

[0052] 2. The bio-based flame retardant prepared in the present invention can significantly improve the flame retardancy of natural rubber. Relying on the free radical capture effect in the gas phase and the charring effect in the condensed phase of the flame retardant, adding only 15 parts can enable the natural rubber composite to exhibit excellent flame retardant properties, such as the vertical burning rating reaching V-0 and the limiting oxygen index (LOI) increasing to 29%.

[0053] 3. The bio-based flame retardant prepared in the present invention can have a strong interfacial bonding force with the matrix through interfacial modification, so the mechanical properties of the natural rubber composite are maintained well.

[0054] This application realizes the preparation of an environmentally friendly flame retardant with bio-based raw materials as the main raw materials. Due to the use of renewable bio-based raw materials, the dependence on petroleum resources is reduced. At the same time, by reacting with phosphorus-containing monomers, the bio-based monomers are endowed with flame retardant properties, avoiding the environmental pollution problems of traditional halogen-based flame retardants. In addition, the bio-based flame retardant has good compatibility with natural rubber and can achieve effective flame retardancy at a lower addition amount, overcoming the disadvantage that inorganic flame retardants require a high addition amount and cause a decline in material properties.

[0055] The bio-based flame retardant and the natural rubber molecular chains form a uniform dispersion system through physical blending. During the combustion process, the phosphorus-based components catalyze charring and the gas-phase dilution effect cooperate to inhibit flame propagation, and the flame retardant efficiency is significantly improved. On the basis of maintaining the original mechanical properties of natural rubber, this composite material meets the UL94 V-0 level flame retardant standard, and the preparation process conforms to the principles of green chemistry. The above embodiments merely represent several implementation manners of the present application. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several variations and improvements can still be made, and these all fall within the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

[0056] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of a bio-based environmental protection flame retardant, characterized in that: It includes raw material selection and operation and treatment reactions based on the selected raw materials. The raw materials include polyhydroxy biobased monomers, polyamino biobased monomers, and phosphorus-containing monomers. The operation and treatment reaction method based on the selected raw materials is to react the polyhydroxy biobased monomer with the phosphorus-containing monomer to obtain a biobased flame retardant; or react the polyamino biobased monomer with the phosphorus-containing monomer to obtain a biobased flame retardant.

2. The preparation method of a bio-based environmental protection flame retardant according to claim 1, characterized in that: The phosphorus-containing monomer is diphenyl chlorophosphate or diphenylphosphoryl chloride. The polyhydroxy biobased monomer or polyamino biobased monomer reacts with diphenyl chlorophosphate or diphenylphosphoryl chloride respectively to obtain a biobased flame retardant.

3. The preparation method of a bio-based environmentally friendly flame retardant according to claim 2, characterized in that: The polyhydroxy biobased monomer is ellagic acid or catechin. Reacting the polyhydroxy biobased monomer with the phosphorus-containing monomer to obtain a biobased flame retardant includes: Reacting ellagic acid with diphenyl chlorophosphate in a molar ratio of 1:2 to obtain a biobased flame retardant. Reacting ellagic acid with diphenylphosphoryl chloride in a molar ratio of 1:2 to obtain a biobased flame retardant. Reacting catechin with diphenyl chlorophosphate in a molar ratio of 1:3 to obtain a biobased flame retardant. Reacting catechin with diphenylphosphoryl chloride in a molar ratio of 1:3 to obtain a biobased flame retardant.

4. The preparation method of a bio-based environmentally friendly flame retardant according to claim 2, characterized in that: The polyamino biobased monomer is spermidine or L-arginine. Reacting the polyamino biobased monomer with the phosphorus-containing monomer to obtain a biobased flame retardant includes: Reacting spermidine with diphenyl chlorophosphate in a molar ratio of 1:1 to obtain a biobased flame retardant. Reacting spermidine with diphenylphosphoryl chloride in a molar ratio of 1:1 to obtain a biobased flame retardant. Reacting L-arginine with diphenyl chlorophosphate in a molar ratio of 1:1 to obtain a biobased flame retardant. Reacting L-arginine with diphenylphosphoryl chloride in a molar ratio of 1:1 to obtain a biobased flame retardant.

5. The preparation method of a bio-based environmental protection flame retardant according to claim 3, characterized in that: The preparation method of the biobased flame retardant obtained by reacting ellagic acid with the phosphorus-containing monomer is as follows: Dissolve a preset amount of ellagic acid and the phosphorus-containing monomer in tetrahydrofuran respectively to obtain corresponding solutions, where the molar ratio of ellagic acid to the phosphorus-containing monomer is 1:

2. Add the ellagic acid solution to a container, and at the same time, drop the phosphorus-containing monomer solution into the ellagic acid solution drop by drop through a constant pressure dropping funnel, and control the reaction temperature at 0-5 °C through an ice-water bath. After the dropping of the phosphorus-containing monomer solution is completed, raise the reaction temperature to 80-120 °C and react for 5-10 h. After the reaction is completed, drop the solution in the container into ethyl acetate, and the reaction product precipitates and settles. The biobased flame retardant is obtained through filtration, washing with water, and drying.

6. The preparation method of a bio-based environmentally friendly flame retardant according to claim 3, characterized in that: The preparation method of the biobased flame retardant obtained by reacting catechin with the phosphorus-containing monomer is as follows: Dissolve a preset amount of catechin and the phosphorus-containing monomer in tetrahydrofuran respectively to obtain corresponding solutions, where the molar ratio of catechin to the phosphorus-containing monomer is 1:

3. Add the catechin solution to a container, and at the same time, drop the phosphorus-containing monomer solution into the catechin solution drop by drop through a constant pressure dropping funnel, and control the reaction temperature at 0-5 °C through an ice-water bath. After the dropping of the phosphorus-containing monomer solution is completed, raise the reaction temperature to 80-120 °C and react for 5-10 h. After the reaction is completed, drop the solution in the container into ethyl acetate, and the reaction product precipitates and settles. The biobased flame retardant is obtained through filtration, washing with water, and drying.

7. The preparation method of a bio-based environmental protection flame retardant according to claim 4, characterized in that: The preparation method of the bio-based flame retardant prepared by the reaction of spermidine and a phosphorus-containing monomer is as follows: Dissolve a preset amount of spermidine and a phosphorus-containing monomer in toluene respectively to obtain corresponding solutions, where the molar ratio of spermidine to the phosphorus-containing monomer is 1:1; Add the spermidine solution into a container, and at the same time, dropwise add the phosphorus-containing monomer solution into the spermidine solution through a constant pressure dropping funnel, and control the reaction temperature at 0-5 °C by an ice-water bath; After the addition of the phosphorus-containing monomer solution is completed, raise the reaction temperature to 80-120 °C and react for 5-10 h; After the reaction is completed, drop the solution in the container into ethyl acetate, and the reaction product precipitates and settles. The bio-based flame retardant is obtained by filtration, washing with water and drying.

8. The preparation method of a bio-based environmentally friendly flame retardant according to claim 4, characterized in that: The preparation method of the bio-based flame retardant prepared by the reaction of L-arginine and a phosphorus-containing monomer is as follows: Dissolve a certain amount of L-arginine and a phosphorus-containing monomer in toluene respectively to obtain corresponding solutions, where the molar ratio of L-arginine to the phosphorus-containing monomer is 1:1; Add the L-arginine solution into a container, and at the same time, dropwise add the phosphorus-containing monomer solution into the L-arginine solution through a constant pressure dropping funnel, and control the reaction temperature at 0-5 °C by an ice-water bath; After the addition of the phosphorus-containing monomer solution is completed, raise the reaction temperature to 80-120 °C and react for 5-10 h; After the reaction is completed, drop the solution in the container into ethyl acetate, and the reaction product precipitates and settles. The bio-based flame retardant is obtained by filtration, washing with water and drying.

9. A flame-retardant modified natural rubber based on a bio-based environmentally friendly flame retardant, characterized in that: The bio-based flame retardant prepared by using the preparation method of a bio-based environmentally friendly flame retardant according to any one of claims 1-8 is mixed with natural rubber to obtain a flame-retardant natural rubber composite material.

10. A flame-retardant modified natural rubber based on a bio-based environmental protection flame retardant according to claim 9, characterized in that: The specific preparation method of the flame-retardant natural rubber composite material is as follows: Plasticize the natural rubber raw rubber on an open mill at 80-100 °C for 10-20 min; Then add 1-2 parts of stearic acid, 4-6 parts of zinc oxide, 0.5-1 part of antioxidant and 1-2 parts of accelerator, and continue to open mill until the rubber compound is uniform; Then add 5-15 parts of the bio-based flame retardant to the rubber compound, continue to open mill for 20-40 min, the roller speed is 150-200 rpm, and then cool to 50-60 °C; Add 1-3 parts of vulcanizing agent and 10-20 parts of carbon black, and continue to mix for 15-20 min; Finally, vulcanize at 140-160 °C on a flat vulcanizer for 5-10 min, and the pressure is 5-15 MPa to obtain the flame-retardant natural rubber composite material.

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